1. Field of the Invention
The present invention relates to a plastic molded type semiconductor device, and more particularly, to a multichip plastic molded type semiconductor device.
2. Description of the Related Art
A multichip plastic molded type semiconductor device in which a plurality of semiconductor chips are sealed in a package is conventionally known.
In conventional multichip plastic molded type semiconductor devices, there is a semiconductor device in which a plurality of logic element chips, each having low current consumption, are sealed, and a semiconductor device in which a plurality of high-power element chips, each having high current consumption, are sealed. However, in the conventional semiconductor device, semiconductor chips of different types such as a logic element chip and a high-power element chip, cannot be sealed in the same package.
In a conventional multichip semiconductor device, semiconductor devices to be sealed are classified by current consumption, and chips of the same type are sealed in one package due to the following reason.
A high-power element chip having high current consumption must have a heat radiating fin for radiating heat generated from the chip. The fin is used as a common mounting region, bed portion, for semiconductor chips. For this reason, in order to have uniform chip potentials of a plurality of chips, chips of the same type must be mounted. If a logic element chip having low current consumption is mounted on the heat radiating fin serving as the bed portion, the logic element chip is influenced by heat generated from a high-power element chip which causes degradation of electric characteristics of the logic element chip or a change in its characteristics.
In addition, the heat radiating fin, serving as the bed portion, is normally made of a conductive material such as a metal. Therefore, when a plurality of semiconductor chips are mounted on the heat radiating fin, these chips are difficult to electrically isolate from each other. As a countermeasure to this, the semiconductor chips may be fixed on the heat radiating fin using an insulating substrate or an insulating paste. For example, in a multichip plastic molded type semiconductor device constituted by only a plurality of high-power element chips, the former method, i.e., the method using an insulating substrate, can be employed in a multichip plastic molded type semiconductor device constituted by only a plurality of high-power element chips. However, since the insulating substrate is used, production cost is increased. Thus, this method does not provide low-price products. On the other hand, in the latter method, since the insulating paste is used, an electrode cannot be extracted from the lower surface of the semiconductor chip.
Since the high-power element chip generates a large amount of heat and an electrode must be extracted from the lower surface of the semiconductor chip, a fixing method by soldering or a eutectic die bonding method, which has excellent ohmic characteristics and thermal conductive characteristics, is used as a means for fixing a semiconductor chip on a bed portion. Contrasted to this, in a logic element chip which generates a small amount of heat, in order to obtain an inexpensive product, bonding using a conductive adhesive is used. For this reason, if a multichip plastic molded type semiconductor device, in which a high-power element chip and a logic element chip are hybridized, is formed, the assembling process is complicated due to different die bonding methods for different types of chip, thereby increasing production cost. In addition, conductive adhesive has poor thermal resistance which causes degradation of the adhesive and a change in the properties of the adhesive.
Even if one die bonding method is used, characteristics of the chips are degraded, and the production cost is increased.
As described above, conventionally, a multichip plastic molded type semiconductor device, in which a plurality of semiconductor chips of different types such as a high-power element chip and a logic element chip are sealed in a single package, is difficult to realize.
In addition, in a multichip plastic molded type semiconductor device, in which only a plurality of high-power element chips are sealed, an insulating substrate must be used, and the product is expensive. High-power element chips of different types are difficult to be mounted in a single package.